Plasma rotation and NTM onset driven by central EC deposition in TCV tokamak

The effects of the central electron cyclotron heating (ECH) and current drive (ECCD) on the spontaneous plasma rotation and on the presence of Tearing Modes (TM), observed in the TCV tokamak[1], were recently investigated as an interplay between the toroidal velocity and NTM onset in absence of sawteeth, ELMs and error fields [2–3]. In a set of reproducible TCV discharges (Ip∼ −150 kA, Bt∼ −1.4 T, ne,av∼ 1.5 1019 m−3, Te∼ 3 keV and Ti∼0.25 keV, q95∼5.8) with both pure EC heating and current drive the cnt-Ip toroidal velocity was observed to be reduced with subsequent co-Ip appearance of 3/2 and 2/1 modes during the ramp up EC phases. The understanding of the capability of the on-axis EC power to modify the rotation profiles before and after the TM onset and of the sudden disappearance of 3/2 mode when 2/1 starts is the main purpose of this work. The velocity profile modifications are due to a direct effect of the EC absorbed power and also related to some variation of the perpendicular diffusion of the to...